Recovery of accurate T2 from historical 1.5 tesla proton density and T2-weighted images: Application to 7-year T2 changes in multiple sclerosis brain

Objective: To determine accurate quantitative transverse relaxation times (T-2) using retrospective clinical images and apply it to examine 7-year changes in multiple sclerosis (MS) brain. Methods: A method for T-2 mapping from retrospective proton density (PD) and T-2-weighted fast spin echo images was recently introduced, but requires measurement of flip angles. We examined whether 1.5 T flip angle variation in brain can be predicted, thus enabling T-2 analysis of historical PD and T-2-weighted images without a concurrent flip angle map. After method validation in healthy volunteers, retrospective longitudinal T-2 analysis was performed in 14 MS subjects over seven years. Changes in patient T2 values were compared with brain atrophy, T-2 lesion load and disability score in MS. Results: Similar flip angle maps across volunteers enabled retrospective T-2 from PD and T-2-weighted images even when different refocusing angles were used. Over seven years, significant T-2 changes of 2-4% were observed when using T-2 modelling and the 7-year effect size for globus pallidus T-2 was 0.56, which was more significant than brain atrophy. No significant T-2 results were found when using exponential fit, which cannot account for refocusing angle variation. Moreover, change is T-2 in globus pallidus and internal capsule correlated with MS disability score over time when using T-2 modelling. Conclusions: Accurate quantitative T-2 can be extracted from standard clinical 1.5 T MRI exams that include PD and T-2-weighted imaging even when no flip angle map is available. This method was applied retrospectively to examine seven year changes in MS. (C) 2016 Elsevier Inc. All rights reserved.